The present invention relates to an improved method of preparing polyamines and the high molecular weight polyamine products obtained therefrom. More particularly, the present invention is directed to an improved process for making high molecular weight polyamines by reacting an amine and an alkylene dihalide in the presence of a self-limiting neutralizing agent which enables the reaction to run its course under generally constant alkaline pH conditions.
In many applications, the usefulness and efficiency of polyamines is directly related to the molecular weight and linearity of the polyamine molecule. Generally, it has been found that improvements or increases in such molecular characteristics as molecular weight and linearity are associated with superior polyamine activity. These molecular characteristics have been found to be especially significant in connection with the use of polyamines in the coagulation of suspended solids from water.
Since the significance of polyamine molecular weight and linearity are well recognized, it follows that those concerned with the synthesis of polyamines are most interested with discovering ways in which to enhance both of these characteristics.
Prior art methods of preparing polyamines by reacting lower amines with alkylene dihalides have exhibited a number of drawbacks. Some of these methods are capable only of producing polymer products of relatively low average molecular weight. Others of these methods can produce high molecular weight polymers, but require precise control and manipulation of the alkalinity of the reaction environment to avoid polymer degradation.
A good example of a method capable of producing high molecular weight polyamines under carefully controlled alkalinity conditions appears in U.S. Pat. No. 3,372,129 to Kenneth G. Phillips, one of the co-inventors of the present improved method of polyamine synthesis. The method of the U.S. Pat. No. 3,372,129 patent entails the reaction of ethylene and 1,2-propylene dihalides with amines in a reaction zone. This method requires that, during at least the terminal 60% of the time of reaction, sufficient basic reagent be introduced into the reaction zone to maintain the reaction pH between about 8.0 and 12.5.
Unfortunately, when polyamine synthesis is carried out on a commercial scale following the teaching of U.S. Pat. No. 3,372,129 or similar variable alkalinity methods, it is quite difficult if not impossible to maintain the pH in the desired range throughout the entire reaction mixture. Localized excesses and deficiencies in alkaline concentration occur due to non-uniform mixing and due to the necessary lag time between adding the basic reagent to the reaction mixture and measuring the pH. When pH falls below the desired range, the rate of polymerization slows or stops resulting in the production of low molecular weight polymers. Localized excesses of basic reagent, on the other hand, degrade the polymer already produced thereby reducing the average molecular weight of the end product.
It would therefore be of benefit to the art if a method were devised of synthesizing polyamines of higher molecular weight and enhanced linearity than was heretofore achieved by prior art techniques. Further important benefits would be obtained if this method eliminated the precise alkalinity control required in the practice of some of the prior art methods.
Since quaternary polyamines may be obtained by quaternizing polyamines, important benefits can be derived from the present invention in connection with the synthesis of polyquaternaries. The overall synthesis process will be improved by the practice of the present invention and the linearity and molecular weight of the end product enhanced.
Other objects and advantages of the present invention will appear hereinafter.